Much attention has been directed towards improving the safety of persons who work at high elevations by providing them with protective devices, such as safety harnesses and lanyards, to suspend them in the event of an accidental fall. However, little emphasis has been placed on how to minimize potential injuries to a person who has fallen and is suspended in a safety harness. One of the most serious risks of injury or death to such a person is created by a condition known as “suspension trauma.” Suspension trauma is a subset of phenomenon known as “orthostatic intolerance” which is caused by a reduction in the circulation of blood throughout the body. More information on this condition is provided by the Occupational Health and Safety Administration's Safety Health and Information Bulletin SHIB 03-24-2004, incorporated herein by reference.
A typical safety harness 100 is shown in FIG. 2. The harness 100 includes a pair of shoulder straps 104 crossing over the shoulders and chest of the wearer and a pair of leg straps 106 extending between and around the legs of the wearer. The shoulder straps 104 and leg straps 106 are attached, such as by side buckles and buckle connectors, to a waist strap 108. The waist strap 108 is connected to a vertical support strap 110. The support strap 110 typically is affixed to a rear dorsal, attachment “D”-ring 112 at its upper end. A safety line or lanyard 102 is connected to the attachment “D’-ring 112 to support the user in the event of a fall. Examples of a safety harness are shown in U.S. Pat. Nos. 6,467,851 and 6,739,427.
The lanyard 102 connects a user's safety harness to an anchor point. The typical lanyard incorporates a shock absorbing device, which reduces the arresting forces during a fall. The shock absorber actually tears and elongates to absorb the force. This can cause the lanyard to lengthen, such as from six feet to almost nine and one-half feet, depending on the weight of the user and the distance of the fall. The user could be hanging as much as nine and one-half feet below the anchor point.
Normally anytime a user has fallen and deployed the shock absorber, rescue becomes difficult. This results in the user being subjected to a physically unsafe condition while the rescue is being carried out. Rescuers often time have trouble reaching the victim; meanwhile the victim is in great peril.
Because a person suspended in a safety harness and lanyard is in a sedentary position, blood can accumulate in the veins, which is commonly called “venous pooling.” This can reduce the circulation of blood and the amount of oxygen provided to the brain and other vital organs. Venous pooling typically occurs in the legs due to the leg straps 106 and the force of gravity caused by the weight of the person suspended in the leg straps 106. Also there is a lack of movement by the person during suspension. In the veins, blood normally is moved back to the heart through one-way valves using the normal muscular action associated with limb movement. If the legs are immobile, then these “muscle pumps” do not operate effectively, and blood can accumulate. Since veins can expand, a large volume of blood may accumulate in the veins.
The leg straps 106 act like tourniquets cutting off circulation in the legs causing an accumulation of blood in the legs thereby reducing the amount of blood in circulation. The body reacts to this reduction by speeding up the heart rate in an attempt to maintain sufficient blood flow to the brain. If the blood supply is significantly reduced, this reaction will not be effective. The body will abruptly slow the heart rate and blood pressure will diminish in the arteries. During severe venous pooling, the reduction in blood and oxygen flowing to the brain causes fainting. This reduction also can have an effect on other vital organs, such as the kidneys. The kidneys are very sensitive to blood oxygen, and renal failure can occur with excessive venous pooling. If these conditions continue, they potentially may be fatal.
Orthostatic intolerance may occur in many different situations where a person remains stationary for an extended period of time with the heart above the legs. One well-known example of orthostatic intolerance is that of a person who faints while standing for a long period of time with his or her “knees locked” (which reduces muscle usage, and therefore, blood circulation). In that case, the moment the person loses consciousness; he or she collapses into a horizontal position. With the legs, heart, and brain on the same level, blood is returned to the heart and blood and oxygen are returned to the brain and other vital organs. Assuming no injuries are caused during the collapse, the individual will quickly regain consciousness and recovery is likely to be rapid.
Persons using fall arrest systems may also experience orthostatic intolerance or suspension trauma. After a fall, a person may remain suspended in a harness for an extended period of time. Depending on the length of time the person is suspended and the level of venous pooling, the resulting orthostatic intolerance may lead to serious injury or even death. Orthostatic intolerance presents a greater threat of injury or death to a person suspended in a safety harness than to a person who faints while standing. The risk is increased because workers suspended in a safety harness will not fall into a horizontal position if they faint, as they would if they fainted while standing. Therefore, there is no “self-correction” mechanism for a worker suspended in a harness, as there is for a person who faints while standing.
Venous pooling and orthostatic intolerance can also be exacerbated by other circumstances related to the fall. For example, shock or the experience of the event that caused the fall, other injuries, the fit or positioning of the harness, the environmental conditions, and the worker's psychological state, all may increase the onset and severity of the pooling and suspension trauma. While a person suspended in a safety harness and lanyard can reduce the effects of suspension trauma by moving his or her legs, this can quickly become difficult or impossible depending on the physical condition of the person. If measures are not taken to reduce the effects of suspension trauma, the brain, kidneys, and other organs are deprived of oxygen and serious or fatal injury may occur.
A need therefore exists to reduce the effects of suspension trauma due to suspension in a safety harness and lanyard due to a fall and reduce the likelihood of serious or fatal injury to the user.